1. Field of the Invention
This invention relates to applicator devices useful for flame spraying heat fusible, powdered plastic or metal coatings onto a substrate, and more particularly, to a flame spray gun comprising means disposed within the gun for instantaneously controlling the powder feed rate through the gun.
2. Description of Related Art
Many flame spray guns, spray nozzles, torches and the like have previously been disclosed in prior art patents such as U.S. Pat. Nos. 2,125,764; 2,404,590; 2,436,335; 2,544,259; 2,594,222; 2,643,955; 2,794,677; 2,804,337; 2,961,335; 3,073,528; 3,171,599; 3,441,215; 3,460,764; 3,565,345; 4,632,309; 4,835,022; 4,865,252; and 4,934,595.
Some flame spray systems that are useful for coating objects with a thin layer of heat fusible plastic or metal powder employ a hopper having an eductor nozzle disposed at or near its base. Compressed air or another pressurized gas is directed through the eductor nozzle, where it entrains powder drawn from the hopper, and conveys the powder through a flow line to an applicator device such as a flame spray gun.
In various prior art devices, the powder feed rate has been controlled in different ways. U.S. Pat. No. 4,934,595, for example, discloses a pilot valve that is mounted on the hopper body and controls the flow of compressed air through the eductor. The pilot valve is operated by a switch disposed on the flame spray gun. A disadvantage of this system is that once the pilot valve is closed by operating the switch on the applicator device, the flow of pressurized air through the eductor is blocked, and powder is permitted to settle in the flow line between the hopper and the gun. This can in turn contribute to undesirable powder surging when the pressurized air supply to the eductor is subsequently reestablished.
In copending application Ser. No. 07/760,866, filed Sep. 16, 1991, an improved flame spray system is disclosed that utilizes a powder control mechanism comprising a valve disposed in the base of the hopper above the eductor. The valve is operated by a switch disposed on the applicator device, and controls the powder flow into the eductor area independently of the compressed air flow through the eductor. This control system enables the operator to turn off the powder feed and purge the flow line of powder prior to turning off the air flow through the eductor. Although this system avoids the powder surging problems associated with the device disclosed in U.S. Pat. No. 4,934,595, it still suffers the disadvantage of a delay between the time the powder valve is closed and the time that the last powder in the flow line clears the flame spray gun. The delay between operation of the switch controlling the powder valve and the cessation of powder flow through the flame spray gun is proportional to the length of the flow line.
Other prior art devices such as those disclosed, for example, in U.S. Pat. No. 3,441,215 and in FIGS. 3 and 4 of 4,835,022 utilize an integrated powder delivery system in which a powder hopper is attached to the top of the applicator device. Powder is gravity fed into the applicator device through a hand operated valve. A principal disadvantage of these systems is that the powder hopper must be located above and adjacent to the applicator device.
A powder feed system and applicator device are therefore needed that comprise a remote powder storage container and means for providing real time control of powder flow and the powder feed rate through the applicator device. Such apparatus is disclosed herein.